1. Field of the Invention
The present invention relates generally to systems and methods for testing spark plug insulators and, more particularly, to systems and methods for testing breakdown voltage/dielectric strength of spark plug insulators.
2. Description of the Background
Because of the trend of engine downsizing, longer and thinner spark plugs are needed to work with newer engines. These next generation spark plugs require high dielectric strength insulators, which offer reduced dimensions but better or at least equivalent performance when compared to a traditional sparkplug. Typically, ASTM D-149 is used to measure the dielectric strength of insulative materials, which tests the breakdown voltage the insulative material can resist at a certain thickness with a set of parallel electrodes. However, because of the complex geometry of spark plug insulators, as well as the aggressive manufacturing process, there is not always a direct correlation between the performance of the insulator and ASTM D-149 measurements.
In the spark plug industry, there are two most commonly used methods for testing the breakdown voltage/dielectric strength of an insulator, as shown in FIGS. 1, 2A, and 2B. In a first method, as shown in FIG. 1, a system is created with a spark plug assembly including a spark plug insulator 20 surrounding a spark plug center electrode 22. A first end 24 of a first wire contact 26 is wound around an end 28 of the center electrode 22 and a second end 30 of the first wire contact 26 is connected to a high voltage source (not shown), for example, a high voltage system as sold by Hipotronics of Brewster, N.Y. A first end 32 of a second wire contact 34 is wound around an end 36 of the insulator 20 opposite the end 28 of the center electrode 22 and a second end 38 of the second wire contact 34 is connected to a ground contact 40. The entire system is placed in dielectric fluid 42 during testing of a spark plug insulator 20, as shown in FIG. 2.
In a second method, as seen in FIGS. 2A and 2B, a system is created with a spark plug assembly including a spark plug insulator 50 surrounding a spark plug center electrode 52. A tip 54 at a first end of the spark plug center electrode 52 is sealed with epoxy and a ground contact 56 is connected to a portion of a metal shell 57 surrounding the insulator 50 adjacent the tip 54. A second end 58 of the center electrode 52 is connected to a high voltage source 59, for example, a system as sold by Hipotronics of Brewester, N.Y. As with the first test method, the entire system of the second test method is placed in dielectric fluid 42 during testing of a spark plug insulator 50.
The methods of FIGS. 1, 2A, and 2B both involve using dielectric fluid to prevent spark and flashover during testing. Unfortunately, the use of dielectric fluid has limited the temperature capabilities of the tests and imposes confounding effects on dielectric breakdown of the insulator. Furthermore, the design of the electrodes (wire, as seen in FIG. 1, and shell, as seen in FIGS. 2A and 2B) leads to a concentrated electric field in a localized area of the insulator, and hence, the results are not representative of the performance of the insulator as a whole.
Accordingly, there is a need for a system and method for testing insulative materials for use in spark plugs to more accurately determine breakdown voltage/dielectric strength.